In recent years, in a magnetic disk device, a perpendicular magnetic recording system has been adopted to achieve high recording density, large capacity, or miniaturization. In a magnetic disk device of this type, data is recorded by positioning a recording head for perpendicular magnetic recording so as to face a recording surface of a magnetic disk having a recording layer for perpendicular magnetic recording, and causing the recording head to generate a perpendicular magnetic field corresponding to recording data in a predetermined region of the magnetic disk.
The above-described recording head includes a main pole a narrowed portion made of a soft magnetic metal and configured to generate a magnetic field in the perpendicular direction; a return pole disposed opposite to the main pole with a write gap in between, and refluxing the magnetic flux from the main pole to form a magnetic circuit with the main pole; and a coil configured to excite a magnetic flux in the magnetic circuit formed by the main pole and the return pole to generate a recording magnetic field.
In the recording head having the above-described configuration, a high frequency assist element is disposed in the write gap in order to further improve a recording capability. The high frequency assist element generates magnetic resonance by generating specific a high frequency vibration at the time of recording and applying the high frequency vibration to a magnetic recording surface, thereby assisting a response of magnetization reversal. An example of the high frequency assist element includes a spin torque oscillating element (STO: Spin Torque Oscillator).
Incidentally, in order to stably oscillate the high frequency assist element, in the related art, a method of generating a constant bias voltage by a preamplifier in the drive circuit and applying the constant bias voltage to the element so that a constant current density is applied to the element.
However, the high frequency assist elements vary in dimensions due to the difficulty of manufacturing, and thus the elements themselves vary in resistance value correspondingly. If the resistance values of the elements themselves are subjected to variations, the voltage values applied to the element parts will largely vary, and as a result, not only the variations in oscillation characteristics but also the possibility of causing element damage due to excessive voltage application may occur.
Further, not only the resistance values of the high frequency assist elements themselves, but also the influence of the incidental resistance component inherent in the wiring path cannot be ignored. In other words, since the incidental resistance component fluctuates according to the temperature change, the voltage applied to the element portion also fluctuates, which hinders achievement of the constant current density.
The object of the embodiment of the present invention is provide a magnetic disk device capable of stabilizing oscillations by making a voltage applied to the element constant regardless of variations in dimension of the high frequency assist element and temperature characteristics of an incidental resistance component of a wiring path, thereby improving a recording density, and a recording head controlling method.